Simplified telescopic feed leg assembly



Nov. 7, 1961 G. H. FUEHRER SIMPLIEIED TELEscoPIc FEED LEG ASSEMBLY Filed Deo. 24, 1959 EN S 7 fr my ,Y F i 5 5% rcB G United States Patent() 3 007 449 snr/mimmo TErEsCori FEED LEG ASSEMBLY George H. Fuehrer, Downey, Calif., assignor to Thor Power Tool Company, Aurora, Ill., a corporation of Delaware Filed Dec. 24, 1959, Ser. No. 861,966 2 Claims. (Cl, 121-46) This invention relates to push feed drill assemblies of the type utilizing a sinker rock drill supported by a telescopic feed leg effective to advance the drill automatically yas the drilling proceeds, and more particularly to a simplified feed leg unit for use with such an assembly.

The present invention features a simplified, lightweight, rugged, fluid-operated feed leg characterized by its appreciably reduced number of components, long service without need for servicing, and by positive foolproof means for maintaining the components firmly assembled despite the severe vibration and shock treatment to which such units are subjected in normal use. The feed leg assembly disclosed in my United States Patent 2,914,031, granted November 24, 1959, discloses ia feed leg unit vastly superior to prior constructions and fulfilling the foregoing objectives but embodies many more components, is heavier and more costly to construct than is the functionally equivalent structure provided by this invention, as is.

readily apparent upon superficial comparison of the structural details of the two embodiments.

Not only are the tubular stages or piston rods of the present unit made of lightweight aluminum but the pistons supported thereon are formed in one piece from cast steel stock. These pistons are rigidly and inseparably secured to the aluminum piston rods by mating threads coated with a powerful adhesive immune to severmce even by the severe vibrations encountered in the operation of percussive drills. A further feature of the present construction concerns the use of one piece synthetic rubber piston cups of U-Shape in cross-section and unique in that -they may be stretched sufficiently to be pressed over keeper shoulders on the pistons without risk of permanent distortion following which they contract into firm seating engagement in appropriately formed grooves thereby avoiding the need for keeper devices heretofore considered essential.

Accordingly, it is a primary object of the present invention to provide an improved expandable feed leg unit for use with sinker type rock drills, and the like power tools, characterized by its ruggedness, lightweight, simplicity of design and ability to withstand the severest shock and vibration without danger of thecomponents becoming loosened.

Another object of the invention is the provision of a feed leg Iassembly featuring a plurality of telescopically assembled stages each including an aluminum tube some of which have permanently assembled thereto a one piece piston.

Another object of the invention is the provision of a feed leg unit wherein the individual stages comprise a tubular piston rod locked threadedly yassembled to a one piece piston by adhesive material highly resistant to severance under the most severe vibration and shock operating conditions.

These `and other more specific objects will appear upon reading .the following specication and claims and upon considering in connection therewith the attached drawing to which they relate.

Referring now to the drawing in which a preferred embodiment of the invention is illustrated:

FIGURE l is a central longitudinal view through a feed leg unit incorporating a preferred embodiment of the invention;

3,@7Al9 Patented Nov. 7, 1961 FIGURE, 2 is an enlarged fragmentary sectional view through a connection between a piston rod and its piston; and

FIGURE 3 is la fragmentary view of the lower end of the feed leg showing certain of the parts in fully extended position.

Referring more particularly to FIGURE l, there is shown an illustrative embodiment of the invention comprising ya feed leg unit designated generally 10 suitable for use in supporting sinker type rock drills in the manner well known in the art and illustrated by Vway of example in FlGURE l of my United States Patent 2,914,031. Unit 1li comprises a plurality of telescopically arranged tubular piston rods 11, 12 and 13 of suitable high strength lightweight material, as aluminum. A cup-shaped end cap 14 is held detachably assembled to the lower end of the outer or larger diameter tube 11, as by snugly mating threads 15 safeguarded against leakage therepast by one and preferably two suitable scaling gaskets 16 and 17.

Integral with the outer end of cap 14 is a hollow boss 2t) having theadedly secured in the open end thereof a pointed spur 21. Preferably and additionally, there is secured to the base of boss 2li a bifurcated foot 22 well known to those skilled in this art which cooperates with spur 21 under certain operating conditions or which can be used independently of spur 21 in securely supporting the base of the feed leg in the iloor of the mine or elsey where. A well Z3 centrally of the inner end of spur 21 houses a compression spring 24 one end of which bears against the end of an elongated rod 25 projecting into the interior of the feed leg. A collar 27 threaded about the lower end of rod 25 is in adjusted position therealong, as by a pin 28. Collar 27 has a loose sliding lit within well 29 formed in boss 2o and its inner face end is normally held seated against the bottom of well 29 by spring 24. A stop nut 3b threaded over the inner free end of rod 25 is locked against displacement, as by an anchor pin 31 having a press fit in rod 25. As will be explained more fully presently, rod 25 and more particularly nut 30' thereon functions to limit the extension of the intermediate tube or stage 12 of feed leg unit 10.

The inner ends of tubes or piston rods 12 and 13 have rigidly secured thereto one piece generally tubular pistons y35 and 36, respectively. Piston 35 includes a cylindrical portion 37 the outer portion of which has a close sliding lit with the smooth inner surface 38 of tube 11 and its threaded stem end 39 has accurately formed high-strength threads mating with similar threads 40 formed on the inner side wall of intermediate tube 12. Prior to the assembly of threads 39 and 4t), the latter threadsr are coated with a high strength adhesive 41 commercially available on the market and suitableA for forming a failproof joint between steel threads 4i? and aluminum threads 39. The piston threadslcoated with this adhef sive are then assembled into threads 40 in the usual manner until the end of the tube seats under considerable pressure against the shoulder at the end of the cylindrical portion 37 of the piston. To this end, a Spanner wrench lmay have its hooked end seated in well 47 opening through the outer surface of piston 35.

It is pointed out that piston 36 is constructed generally similarly to piston 35. Its larger cylindrical portion 44 has its outer surface in close sliding contact with the inner surface of intermediate stage 12. Likewise, its threaded stem portion 45 is held assembled to threads 46 of tubular pis-ton rod 13 by adhesive in the same manner described above in connection with threads 39 and 40.

Another important feature of pistons 35 and 36 comprises the provision of annular seating grooves 50, 50 axially adjacent frusto-conical surface 51 which surface serves twofold functions. In the first place, this surface 51 acts as a pilot for gradually expanding resilient sealing ring 55 as this ring is pressed axially thereover and into groove 50, an operation performed before the assembly of the feed leg unit. Once sealing ring 55 has been pressed past surface 51 it contracts automatically into snug litting sealing engagement with the bottom of groove 50.

The construction and constituent material of sealing ring 55 is of importance both as respects its assembly and the trouble-free operation of the feed leg. VPreferably, ring 55 is made of a resilient material having high resistance to wear, negligible cold flow characteristics and which will stretch suiciently to override inclined surface 51 Without permanent deformation. A material found highly satisfactory in meeting these and other desirable properties comprises a synthetic elastomeric material known as urethane. The sealing ring is preferably of U-shape in cross-section with the free lip edge of its outer side wall diverging slightly outwardly and having a normal diameter in excess of the cylindrical surface against which it operates so as to be naturally resiliently pressed thereagainst in the operation of the feed leg. The piston rings for both pistons have similar features though differing slightly in diameter for obvious reasons.

The upper ends of the tubular piston rods 11, 12 and 13 are provided with generally conventional bushings and retainers, outer piston rod for the lower stage of the feed leg having an elongated bushing 60 threadedly seated at 61 over the upper end of tube 11 and including an 0- ring gasket 62' to safeguard against fluid leakage. Preferably, a sleeve of suitable bearing material 63 has a close sliding lit with the smooth exterior of the intermediate stage 12 and is held assembled against the upper end of stage 11 by bushing 60. A dust guard and wiper seal 65 is held captive within the outer end of bushing 60 with its lip bearing against the exterior of intermediate stage tube 12 in known manner.

Bushing 70 has threads 71 on its exterior mating with corresponding threads on the inner surface of tube 12 and supports in its outer end a dust guard and seal 72 similar to guard seal 65. It is also pointed out that the inner end 74 of bushing 70 cooperates with a shoulder 75 on piston 36 to limit the extension of the upper stage 13 of the feed leg.

Threadedly seated in the outer end of inner tube 13 is a bushing 80 and an 0ring 81. Provision for securing the upper end of feed leg unit to a sinker drill includes a hollow coupling fitting 82 having a threaded inner end 83 holding it assembled to a tapered passage 84 extending axially of bushing 80. The anged outer end 85 of fitting 82 cooperates with a flanged nut 86 in detachably holding the feed leg coupled to the sinker drill with its pressurized fluid passage in communication with the interior of the feed leg through hollow tting 82.

There remains to be mentioned a feature of larger piston 35 limiting the extension of tube 12 relative to tube 11 and holding these tubes assembled. To this end, piston 35 has a spider 90 threaded axially of its central hub and seating a bushing 91 having a loose sliding fit about rod 25. As is made clear by FIGURE 3, bushing 91 is so adjusted relative to stop nut 30 as to limit the extension of intermediate stage 12 relative to lower stage 11.

Limited lateral movement of rod 25., particularly as respects its upper end, is permitted within lower stage 11 by reason of the yloose connection provided between the rod and Wells 23 and 29. In this manner, close manufacturing tolerances are unnecessary and stage 12 is free to extend through its operating range without interference or binding action between rod 25 and bushing 91.

The manner in which the components are assembled to form the described feed leg unit will be quite apparent from the foregoing detailed description of the structure. Preferably, the adhesive 41 holding the pistons assembled to tubes 12 and 13 is allowed to set for at least 24 hours after assembly before the unit is subjected to pressure testing. This insures that the adhesive has taken a final and rm set such that it will not break down or fail when subjected to the most vigorous operating conditions.

In the use of the feed leg, its upper end 82 is coupled to the sinker drill or other power unit to be supported thereby and pressurized Huid is supplied into the interior of the feed leg through hollow coupling 82 under suitable control well known to those skilled in this art. The quantity and pressure of the fluid so admitted to the unit governs the degree of extension of the several stages, it being noted that this fluid pressure acts on the U-shaped sealing rings 55 to press the inner lip thereof against the Wall of groove 50 and the outer lip against the interior side wall of tubular members 11 and 12. The cement filling all space between mating threads 39 and 40 of the two pistons 35 and 36 provides positive assurance against the loosening or accidental disassembly of these pistons 'from their respective supporting piston rods.

While the particular simplified telescopic feed leg assembly herein shown and disclosed in detail is fully capable of attaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein `shown other than as defined in the appended claims.

I claim:

1. In an extendable feed leg unit of the type employed to support and advance a sinker rock drill and having a plurality of telesoopically assembled tubes, that improvement which comprises a one piece piston having a threaded stern mating with the threaded inner end of one of said tubes and held against reverse rotation relative thereto by an adhesive coating resistant to the severe vibration and shock conditions normally encountered in the use of said feed leg unit.

2. The combination defined in claim 1 characterized in that said feed leg unit includes a plurality of one piece pistons of graduated sizes each held threadedly assembled to the inner threaded end of a different one of said telescopically assembled tubes, and each of said pairs of mating threads `being reinforced and held against unthreading by an intervening film of rmly set adhesive.

References Cited in the file of this patent UNITED STATES PATENTS 2,618,122 Gratzmuller Nov, 18, 1952 2,689,547 Pearson Sept. 21, 1954 2,813,515 Curtis Nov. 19, 1957 2,914,031 Fuehrer Nov. 24, 1959 

